It is very important that you are fitted when shopping for a maternity or nursing bra as soon as there is a noticeable increase in the size of your bust. In the early months of your pregnancy your bra should be fitted on the tightest hook and eye fastenings to allow for further growth across the back and diaphragm. The cup should also allow room for extra growth of the bust. As a guide, you should be able to slide your hand into the upper section of the cup to assess if there is enough room for expansion.